Process for producing propylene oxide

ABSTRACT

A process for producing propylene oxide, which comprises steps described below, wherein the concentration of ethylbenzene in a solution containing isopropylbenzene to be recycled to the oxidation step is 10% by weight or less: 
     oxidation step; a step in which isopropylbenzene is oxidized to obtain isopropylbenzene hydroperoxide, 
     epoxidation step; a step in which isopropyl hydroperoxide obtained in the oxidation step is reacted with propylene to obtain propylene oxide and cumyl alcohol, and 
     hydrogenolysis step; a step in which cumyl alcohol obtained in the epoxidation step is subjected to hydrogenolysis to obtain isopropylbenzene, and said isopropylbenzene is recycled to the oxidation step as a raw material for the oxidation step.

This application is a 371 of PCT/JP01/02190 filed on Mar. 19, 2001.

TECHNICAL FIELD

The present invention relates to a process for producing propyleneoxide. More particularly, the invention relates to a process forproducing propylene oxide, wherein said process for producing propyleneoxide has excellent characteristics that propylene is converted topropylene oxide using isopropylbenzene hydroperoxide obtained fromisopropylbenzene, as an oxygen carrier, that said isopropylbenzene canbe repeatedly used, that the reaction volume in each step can beeffectively utilized, and that epoxidation reaction can be effectivelycarried out thereby being able to produce propylene oxide effectively.

BACKGROUND ART

A process in which propylene is oxidized using ethylbenzenehydroperoxide as an oxygen carrier to give propylene oxide and styreneis known as Halcon process. Since, in this process, styrene isinevitably produced together with propylene oxide, it is unsatisfactoryfrom the viewpoint that only propylene oxide is to be selectivelyproduced.

On the other hand, a concept of a process in which propylene isconverted to propylene oxide using isopropylbenzene hydroperoxideobtained from isopropylbenzene, as an oxygen carrier, and saidisopropylbenzene is repeatedly used, is described in Czechoslovak PatentNo. CS 140,743. The process described in said patent does not containprecise descriptions concerning necessary steps except an oxidationstep, epoxidation step and hydrogenolysis step. Various problems arisein practical recycling of isopropylbenzene and therefore thedescriptions cannot be said as sufficient for industrial realization.

DISCLOSURE OF THE INVENTION

Under such circumstances, an object of the present invention is toprovide a process for producing propylene oxide, having excellentcharacteristics that propylene is converted to propylene oxide usingisopropylbenzene hydroperoxide obtained from isopropylbenzene, as anoxygen carrier, that said isopropylbenzene can be repeatedly used, thatthere action volume in each step can be effectively utilized, and thatepoxidation reaction can be effectively carried out thereby being ableto produce propylene oxide effectively.

Namely, the invention relates to a process for producing propyleneoxide, which comprises steps described below, wherein the concentrationof ethylbenzene in a solution containing isopropylbenzene to be recycledto the oxidation step is 10% by weight or less:

oxidation step; a step in which isopropylbenzene is oxidized to obtainisopropylbenzene hydroperoxide,

epoxidation step; a step in which isopropyl hydroperoxide obtained inthe oxidation step is reacted with propylene to obtain propylene oxideand cumyl alcohol, and

hydrogenolysis step; a step in which cumyl alcohol obtained in theepoxidation step is subjected to hydrogenolysis to obtainisopropylbenzene, and said isopropylbenzene is recycled to the oxidationstep as a raw material for the oxidation step.

BEST MODE FOR CARRYING OUT THE INVENTION

The oxidation step in the present invention is a step in whichisopropylbenzene is oxidized to obtain isopropylbenzene hydroperoxide.The oxidation of isopropylbenzene is usually effected by autoxidationwith oxygen-containing gas such as the air, an oxygen-enriched air orthe like. The oxidation reaction may be carried out without any additiveor with an additive such as an alkali. The reaction temperature isusually 50 to 200° C., and the reaction pressure is usually between theatmospheric pressure and 5 MPa. In the oxidation with an additive, thealkali includes alkali metal compounds such as NaOH, KOH; alkaline earthmetal compounds; alkali metal carbonates such as Na₂CO₃, NaHCO₃;ammonia; (NH₄)₂CO₃; alkali metal ammonium carbonates and the like.

The epoxidation step in the present invention is a step in whichisopropylbenzene hydroperoxide obtained in the oxidation step is reactedwith propylene to obtain propylene oxide and cumyl alcohol. From aviewpoint that the desired product should be obtained in a high yieldand under a high selectivity, the epoxidation step is preferablyconducted in the presence of a catalyst containing a titanium-containingsilicon oxide. The catalyst is preferably a catalyst containing titaniumchemically bound to silicon oxide, so-called titanium-silica catalyst.Examples may include products in which a titanium compound is supportedon a silica carrier, products in which a titanium compound is compoundedwith a silicon oxide by a co-precipitation or sol-gel method,titanium-containing zeolite compounds or the like.

In the present invention, isopropylbenzene hydroperoxide used as the rawmaterial for the epoxidation step may be a dilute or thick purificationor non-purification product.

The epoxidation reaction is carried out by contacting propylene andisopropylbenzene hydroperoxide with a catalyst. The reaction can beconducted in a liquid phase using a solvent. The solvent must be aliquid under the reaction temperature and pressure, and substantiallyinert to the reactants and the product. The solvent may be composed of asubstance existing in a solution of the hydroperoxide used. When, forexample, isopropylbenzene hydroperoxide is a mixture withisopropylbenzene as the raw material, it is also possible to use saidmaterial, without adding a solvent in particular, as the solvent. Otheruseful solvents include aromatic single-ring compounds (for example,benzene, toluene, chlorobenzene and o-dichlorobenzene), alkane (forexample, octane, decane and dodecane) and the like. The epoxidationtemperature is generally 0 to 200° C. and preferably 25 to 200° C. Thepressure may be any pressure sufficient to keep liquid state of thereaction mixture. Generally, the pressure is advantageously 100 to10,000 kPa.

The epoxidation can advantageously be carried out with a catalyst in theform of a slurry or a fixed-bed. The fixed-bed is preferred in the caseof a large-scale industrial operation. In addition, the reaction can becarried out by a batch process, a semi-continuous process, a continuousprocess or the like. When a liquid containing the raw materials forreaction is passed through a fixed-bed, the catalyst is not contained atall or substantially in a liquid mixture discharged from a reactionzone.

The hydrogenolysis step in the present invention is a step in whichcumyl alcohol obtained in the epoxidation step is subjected tohydrogenolysis to obtain isopropylbenzene, and said isopropylbenzene isrecycled to the oxidation step as the raw material for the oxidationstep. In other words, the same product, i.e. isopropylbenzene, used inthe oxidation step is recovered. The hydrogenolysis is usually carriedout by contacting cumyl alcohol and hydrogen with a catalyst. Thereaction can be conducted in a liquid phase using a solvent or in agaseous phase. The solvent must be substantially inert to the reactantsand the product. The solvent may comprise a substance existing in asolution of the cumyl alcohol used. When, for example, cumyl alcohol isa mixture with isopropylbenzene as the product, it is possible to usethis, without adding a solvent in particular, as the solvent. Otheruseful solvents include alkane (for example, octane, decane anddodecane), aromatic single-ring compounds (for example, benzene,ethylbenzene and toluene), and others. The temperature for thehydrogenolysis reaction is generally 0 to 500° C. and preferably 30 to400° C. Generally, the pressure is advantageously 100 to 10,000 kPa. Thehydrogenolysis can advantageously be carried out with a catalyst in theform of a slurry or a fixed-bed. Any catalyst having a hydrogenationability can be used as the catalyst. Examples of the catalyst includemetal catalysts of metals of the group 8th to 10th such as cobalt,nickel, palladium and the like, and metal catalysts of metals of thegroup 11th or 12th such as copper, zinc and the like, and coppercatalysts are preferred from the viewpoint that by-products aresuppressed. The copper catalysts include copper, Raney copper,copper-chromium, copper-zinc, copper-chromium-zinc, copper-silica,copper-alumina and the like. The process of the present invention can becarried out by a batch process, a semi-continuous process or acontinuous process. When a solution or gas containing the raw materialsfor reaction is passed through a fixed-bed, the catalyst is notcontained at all or substantially in a liquid mixture discharged fromthe reaction zone.

In the present invention, it is necessary that the concentration ofethylbenzene in a solution containing isopropylbenzene to be recycled tothe oxidation step is controlled to 10% by weight or less, preferably 5%by weight or less. Ethylbenzene is produced in the hydrogenolysis stepas the result of hydrogenation of acetophenone which is formed bydecomposition of isopropylbenzene hydroperoxide in the oxidation stepand epoxidation step. Ethylbenzene is a component accumulated in thesystem, and its concentration increases with time by continuousrecycling. This cause a decrease in effective reaction volume in each ofthe steps, and inhibition of the reaction in the epoxidation step due toby-products derived from ethylbenzene as well as an inconvenience thatsaid by-products might be impurities in propylene oxide. Inconsideration of effective utilization of the reaction volume andsuppression of by-products, it is necessary to control the concentrationof ethylbenzene in the solution containing isopropylbenzene to berecycled to the oxidation step within a range specified in the presentinvention. Methods for controlling the concentration of ethylbenzene maybe anyone of methods in which all or part of ethylbenzene is removed tooutside of the system of steps in the preset invention by distillation,extraction or the like, methods in which the compound is converted toanother compound, methods in which the concentration of the compound islowered by an adsorbent or the like, and so on. In the case of removalto outside of the system, the step for removing ethylbenzene(hereinafter, may be referred to as “ethylbenzene-removing step”) can becarried out in at least one place of the oxidation step, epoxidationstep and hydrogenolysis step or in at least one place between which thesteps are connected, usually by distillation, extraction or the like,and it is preferred to carry out distillation after the hydrogenolysisstep in which a difference between boiling points of the usefulcomponent and ethylbenzene become the largest, from viewpoints ofdecreasing loss of the useful component and of minimizing energy fordistillation. Moreover, in the present invention, the concentration oforganic acids in the solution containing isopropylbenzene hydroperoxideto be supplied to the epoxidation step is preferably 0.5% by weight orless and more preferably 0.1% or less. By specifying within this range,the activity of the catalyst used in the epoxidation step can bemaintained at a high level and the life of the catalyst can be kept forlonger time.

Additionally, in the present invention, the concentration of phenol inthe solution containing isopropylbenzene to be recycled to the oxidationstep is preferably 5% by weight or less. These allow effectiveutilization of the volume for the reaction in each step and effectiveaccomplishment of oxidation reaction and epoxidation reaction.

Moreover, in the present invention, the hydrogen ion concentration (pH)in the solution containing isopropylbenzene to be recycled to theoxidation step is preferably 5 to 10. This allows maintenance of theyield in the oxidation step at a high level. Herein, pH refers to avalue obtained by the following measurement: That is, the solution ofisopropylbenzene is mixed with water at a weight ratio of 1:1; aftershaking the mixture sufficiently, pH of an aqueous phase separated outof an oil layer is measured to give the value.

Furthermore, in the present invention, the concentration of cumene dimerin the solution containing isopropylbenzene to be recycled to theoxidation step is preferably 5% by weight or less. This allows effectiveutilization of the volume for the reaction in each step and preventionof stoppage trouble in the system.

EXAMPLE 1

Oxidation Step

Isopropylbenzene recycled from the hydrogenolysis step (wherein theconcentration of ethylbenzene in a solution containing isopropylbenzeneto be recycled to the oxidation step is less than 10% by weight) ismixed with the air and reacted under conditions including a pressure of300 kPa and a temperature of 150° C. for 5 hours. The produced oxidizedsolution has the following composition:

Composition of Oxidation Solution:

isopropylbenzene hydroperoxide 35% by weight cumyl alcohol 2% by weightisopropylbenzene 60% by weight acetophenone 0.1% by weight ethylbenzene0.5% by weight

Epoxidation Step

The oxidized solution which is obtained in the oxidation step, iscontinuously passed through a fixed-bed flowing reactor in the presenceof titanium-containing silicon oxide catalyst together with 10 times bymol of propylene per mol of isopropylbenzene hydroperoxide contained inthe oxidized solution. By controlling the temperature at the inlet, theconversion of isopropylbenzene hydroperoxide is maintained at 99% andstabilized at stationary state. At this state, the reaction temperatureis 60° C. and the selectivity is 95%. Lower boiling components such aspropylene, propylene oxide and the like are separated and recovered. Theobtained reaction solution has the following composition:

Composition of Epoxidized Solution:

isopropylbenzene hydroperoxide 0.4% by weight cumyl alcohol 33.5% byweight isopropylbenzene 62.3% by weight acetophenone 0.6% by weightethylbenzene 0.5% by weight

Hydrogenolysis Step

The reaction solution which is obtained in the epoxidation step iscontinuously passed through a fixed-bed flowing reactor in the presenceof copper-chromium catalyst together with 2 times by mol of hydrogen permol of cumyl alcohol in the reaction liquid. By controlling thetemperature at the inlet, almost 100% of cumyl alcohol is converted. Atthis state, the reaction temperature is 180° C. The obtainedhydrogenolysis solution has the following composition:

Composition of Hydrogenolysis Solution:

isopropylbenzene hydroperoxide 0% by weight cumyl alcohol 0% by weightisopropylbenzene 96.1% by weight acetophenone 0.0% by weightethylbenzene 1.1% by weight

Ethylbenzene-Removing Step

Ethylbenzene is removed from the hydrogenolysis solution obtained in thehydrogenolysis step by distillation. An oil layer which is obtained hasthe following composition:

Composition of Ethylbenzene-Removed Solution:

isopropylbenzene hydroperoxide 0% by weight cumyl alcohol 0% by weightisopropylbenzene 96.6% by weight acetophenone 0.0% by weightethylbenzene 0.5% by weight

COMPARATIVE EXAMPLE 1

When oxidation, epoxidation and hydrogenolysis are carried out undersimilar conditions to those in Example 1 except that removal ofethylbenzene is not carried out. The concentration of ethylbenzene inthe oil layer to be recycled continuously increases. As the result, theconcentration of ethylbenzene in the solution containingisopropylbenzene to be recycled to oxidation step exceeds 10% by weightand effective utilization of the reaction volume in each step becomesimpossible. In addition, the catalyst in the epoxidation step ispoisoned and its activity gradually drops.

INDUSTRIAL APPLICABILITY

As described above, according to the present invention, there can beprovided a process for producing propylene oxide, having excellentcharacteristics that propylene is converted to propylene oxide usingisopropylbenzene hydroperoxide obtained from isopropylbenzene, as anoxygen carrier, that said isopropylbenzene can repeatedly be used, thatthe reaction volume in each step can be effectively utilized, and thatepoxidation reaction can be effectively carried out thereby being ableto produce propylene oxide effectively.

What is claimed is:
 1. A process for producing propylene oxide, which comprises steps described below, wherein the concentration of ethylbenzene in a solution containing isopropylbenzene to be recycled to the oxidation step is 10% by weight or less: oxidation step; a step in which isopropylbenzene is oxidized to obtain isopropylbenzene hydroperoxide, epoxidation step; a step in which isopropyl hydroperoxide obtained in the oxidation step is reacted with propylene to obtain propylene oxide and cumyl alcohol, and hydrogenolysis step; a step in which cumyl alcohol obtained in the epoxidation step is subjected to hydrogenolysis to obtain isopropylbenzene, and said isopropylbenzene is recycled to the oxidation step as a raw material for the oxidation step.
 2. The process according to claim 1, comprising a step for removing ethylbenzene to outside of the system in at least one place of the steps or between which the steps are connected.
 3. The process according to claim 1 or 2, wherein the concentration of ethylbenzene is 5% by weight or less. 